Conventional disk drives for use in work stations, personal computers, and portable computers, are required to provide a large amount of data storage within a minimum physical space. In general, disk drives operate by positioning a read/write transducing head over respective tracks on magnetic recording disks. Positioning of the head over the tracks is accomplished by an actuator coupled to control electronics, which control the positioning of the actuator, rotation of the disks and the read/write functions of the heads. With the advent of portable computers, disk drives are now required to reliably perform in a wide range of environments which may vary substantially with respect to temperature, pressure and humidity.
Conventionally, disk drives had been sealed to prevent pressure changes and to minimize the presence of contaminants within the drive. In order to accomplish this, the above-described components were hermetically sealed within a base and cover. However, where extreme pressure differentials exist between the interior and exterior of the drive, as may be caused at higher or lower elevations or at extreme temperatures, the hermetic seal of the disk drive was often broken, thereby allowing pressure changes and unfiltered contaminant entry into the drive. Attempts to improve the hermetic seal, as for example, by providing a flexible and compressible gasket around the periphery of the drive between the base and cover, have proven somewhat ineffective in totally isolating the interior of the drive from the external environment at extreme pressure and/or temperature conditions.
As result of the difficulty in providing completely sealed drives, some conventional drives have been provided with a breather filter which allows fluid to pass into and out of the drive so as to substantially equalize the internal pressure of the drive to that of the surrounding environment. Thus, fluids passing into the drive from the surrounding environment are filtered to remove contaminants therefrom. While breather filters are able to filter out many particulates from the surrounding atmosphere, they are relatively ineffective in preventing other contaminants from entering into the interior of the drive. For example, breather filters are unable to filter out corrosive gasses that may be found in the atmosphere, such as chlorine, which gasses act to erode the internal disk drive components. Similarly, breather filters are largely unable to prevent water vapor from entering into the interior of the drive. Water vapor can similarly have a corrosive effect on drive components, as well as causing problems such as stiction, where a disk drive head adheres to the disk surface and must be broken free upon start-up of the drive. Further still, while breather filters are largely effective in filtering out particulates, such particulates may buildup within the breather filter over time.
One solution to the problem of atmospheric diffusion into the interior of the drive has been proposed in U.S. Pat. No. 4,751,594 to Blanks, which discloses a serpentinian groove formed in a plate mounted on the cover of the drive. Prior to entering the interior of the drive, fluid from the external environment must pass through the grooves. Largely through control of the diameter of the groove, Blanks discloses that the pressure of the drive interior may be adjusted to that of the external environment while retarding water vapor diffusion into the drive.
Another solution to the problem of atmospheric diffusion is shown in U.S. Pat. No. 5,025,336 to Morehouse et al. In one embodiment of the invention, fluid from the external environment enters through holes in the cover, travels along a groove formed in the cover, and into a compartment which communicates with the interior of the disk drive. A planar desiccant may be provided within the compartment to remove contaminants such that the entering fluid travels through the desiccant from the topside to the bottom side, i.e., through the narrowest dimension of the desiccant. Moreover, there is only a single compartment separating the interior of the drive from the external environment. Similarly, in U.S. Pat. No. 4,620,248 to Gitzendanner, there is disclosed a disk drive including a tube and a desiccant through which fluid from the external environment travels. The tube and desiccant are provided within a single enclosed chamber inside the drive housing, which chamber communicates with the interior of the drive.
During nonoperational periods of the drive, and generally where there is little or no pressure and temperature differential between the interior and exterior of the drive, diffusion of fluid through the diffusion structure still occurs. With conventional diffusion structures having only one compartment, any contaminants from the external environment that diffuse into the compartment may subsequently enter the interior of the drive as result of further diffusion or as result of an influx of fluid into the drive interior upon a relative increase or decrease in external pressure or temperature, respectively.
Moreover, conventional diffusion structures are relatively complicated and/or expensive to manufacture in that they are formed from a number of die cast parts with intricate designs. Furthermore, during the life of a drive, contaminants such as water vapor may buildup within the diffusion tubes. In conventional diffusion structures including a desiccant compartment, while the desiccant removes water vapor from the structure, the desiccant produces particulates which may buildup in the tubes and/or compartment. It is not contemplated in conventional diffusion structures to allow access to the interior of the tubes or desiccant compartment so as to allow cleaning of the tubes or replacement of the desiccant.
Therefore, there is a need for an improved diffusion structure which overcomes the problems found in the prior art.